1. Field of the Invention
The present invention relates to a drilling tool for and a drilling method of drilling bores in rock formations in mines.
2. Description of the Prior Art
In mines, the rock formation is formed of diverse layers. In addition to desired extraction products, e.g., coal, ore, the mine rock formations contain loam layers.
A load applied to a drilling tool varies with varying of the rock formation layers. At a pure manual operation, the tool user should adapt an advancing speed of a drilling head to the layer sequence. In particular, in the loam layers, a slow advance is required so that the glutinous loam is rinsed out of the bore and would not set around the drilling head.
In practice, a tool user has only an approximate knowledge of the position of separate layers. Therefore, the user is forced to work with a small advancing speed.
U.S. Pat. No. 6,637,522 discloses an automated process that should protect the tool from an overload. The bore is rinsed with a pressurized drilling fluid during drilling. A control sensor detects the pressure of the rinsing fluid. An electrical control device controls advance of the drilling head dependent on the measured pressure.
However, in mines, open mines, because of humidity and mechanical loads, the connections and contacts of power supply and control system should meet very stringent requirements. Correspondingly, the costs of an available electrical supply should be taken into account.
An object of the present invention is to provide an automated drilling method and a corresponding drilling tool without use of control electronics.